The present invention relates to vibration damping materials comprising a polymer. The invention further relates to data storage medium prepared from the vibration damping materials.
Vibration damping is essential in many mechanical systems where undesired resonances may be excited by normal perturbations. The suspension system in an automobile, for example, will exhibit large unwanted oscillations in response to road irregularities unless properly damped. Vibration dampers used in automobiles consist of springs providing shock and vibration isolation to a motor vehicle seat assembly. Layers of elastomeric materials that absorb energy are other types of damping material. Polyethylene, polypropylene, non-conjugated dienes, rubber cross linkers and similar materials are examples of these vibration systems. Composites of metal and polymer are employed on the outside of many computer hard disk drives to reduce the noise of the drive within the computer. Vibration dampers are also used in printed circuit boards and spindle motors in internal disk drive applications. In particular, vibration damping materials are used to guard the interior of a disk drive from external shock forces.
Materials used for vibration, damping should exhibit large viscous losses in response to deformation. These losses are typically quantified in terms of either dynamic Young's moduli or dynamic shear moduli. In either case, the dynamic storage modulus, by definition, is proportional to the amplitude of the stress, which results in response to a sinusoidal strain applied in phase with the stress (where the strain may be either shear or elongational depending on whether shear or Young's modulus is desired respectively). Similarly, the loss modulus is, by definition, proportional to the amplitude of the stress, which results in response to the application of a sinusoidal strain rate applied out of phase with the stress. The ratio of dynamic shear loss modulus to dynamic shear storage modulus, or dynamic Young's loss modulus to dynamic Young's storage modulus, at a particular oscillation frequency, is often referred to as tan delta. The magnitude of the loss modulus in a material quantifies its viscous-like resistance to deformation while tan delta quantifies the relative magnitude of this resistance to elastic response. Hereinafter, the quantity tan delta is often referred to as mechanical damping coefficient.
Due to a wide range of possible applications, there has been an intense research in polymer systems capable of damping out vibrations. Most polymer systems have a low fundamental vibration frequency. Many of these systems employ an elastomer in combination with a glassy polymer, metal, or combination thereof which are in contrast to single-phase materials. Thus, it would be desirable to develop damping systems which offer damping at room temperature without the use of a dispersed rubbery phase or to multiple phase polymer systems.
One area in which there has been intense research in polymer systems capable of damping out vibrations is in “first surface” medium. Unlike compact disks (CD) and digital versatile disks (DVD), storage medium having high areal density capabilities, typically greater than 5 Gigabits per square inch, employ first surface or near field read/write techniques in order to increase the areal density. In general, the higher the density sought, the closer the read/write device should be to the surface of the storage medium. Consequently, the axial displacement of the substrate should be sufficiently less than a tolerable system axial displacement distance in order to prevent damage to the read/write device storage medium surface during vibration, shock conditions, or combinations thereof. “First surface” as used herein refers to the data layer, which is on the surface of a substrate wherein an optic does not pass through the substrate. “Near field read/write techniques” as used herein refer to an optical mechanism wherein the number aperture is greater than about 0.08. For such storage medium, the optical quality is not relevant as in the case of CD or DVD, but the physical and mechanical properties of the substrate become increasingly important. The physical characteristics of the storage media when in use can affect the ability to store and retrieve data. For high areal density applications, including first surface applications, the surface quality of the storage medium can affect the accuracy of the reading device, the ability to store data, and replication qualities of the substrate. Furthermore, the physical characteristics of the storage medium when in use can also affect the ability to store and retrieve data by causing the disk to be temporarily out of tilt specification. For instance, if the axial displacement of the medium is too great, the axial displacement can inhibit the accurate retrieval of data and/or damage the read/write device. Thus, improved vibration performance may be achieved by either high modulus or high damping. Conventionally, these have been addressed by utilizing metal, for example, aluminum, and glass substrates. These substrates are formed into a disk and the desired layers are disposed upon the substrate by various techniques.
Vibration concerns and high axial displacement are critical in the design of data storage devices, such as optical disk drives and hard disk drives. Thus, ways to minimize axial displacement, via geometrical design and/or material property changes, are of immense interest. Given that the dimensions of the storage media are specified by the industry for each specific media application, the key area of investigation is the development of materials inherently capable of improved axial displacement. It would also be desirable to develop damping systems utilizing polymers, which are suitable for use in data storage devices, in particular in substrate applications.